1. Field of the Invention
The present invention relates to an improvement of a method for recovering acrylonitrile by absorbing acrylonitrile contained in a gas in water. Particularly, the present invention relates to a method for accelerating dissolution of acrylonitrile into water, so that when the same amount of an absorbing solvent is employed, the amount of acrylonitrile remaining in the gas can be reduced as compared with a conventional method.
2. Discussion of Background
Acrylonitrile is produced in a large scale by ammoxidation of propylene. Further, a method has recently been developed wherein ammoxidation is carried out using a relatively inexpensive propane as a starting material instead of propylene. In a conventional typical method, propylene, ammonia and air are supplied into a fluidized bed reactor and reacted at a high temperature to form acrylonitrile. An effluent gas containing acrylonitrile from the reactor is firstly washed with an aqueous sulfuric acid solution to remove unreacted ammonia in the form of an aqueous ammonium sulfate solution. Then, the gas is cooled and counter-currently contacted with much amount of water, so that acrylonitrile as well as hydrogen cyanide and other by-product organic substances, will be dissolved in water and separated from the light gas. From the aqueous solution having acrylonitrile, etc., dissolved, purified acrylonitrile is obtained by a proper combination of such means as stripping and distillation. It is important for this method to simultaneously satisfy such requirements that the amount of acrylonitrile remaining in the light gas should be minimized when acrylonitrile contained in the gas is dissolved in water and separated from the light gas and that the concentration of acrylonitrile in the resulting aqueous solution should be as high as possible. Acrylonitrile remaining in the light gas will be wasted as a loss, and the amount being large means a decrease in the yield. Recovery of purified acrylonitrile from the obtained aqueous solution is carried out by a combination of such means as stripping and distillation, as mentioned above. Accordingly, if the acrylonitrile concentration in the aqueous solution is low, the apparatus for stripping and distillation are obliged to be large, and the energy consumption will accordingly be increased.